FIG. 1 illustrates an exemplary fuel cell. This fuel cell 101 is a solid oxide fuel cell, and generates electric power by using a fuel gas such as a town gas, water, and air. The fuel cell 101 includes an evaporator 102, an air preheater 103, a fuel reformer 104, a burner 105, a power generation cell 106, and other elements.
The evaporator 102 heats water to generate a water vapor. The generated water vapor is mixed with a fuel gas that is, e.g., desulfurized, and is subsequently sent to the fuel reformer 104. In the fuel reformer 104, the mixed gas of a fuel gas and a water vapor is reformed into a high temperature reformed gas primarily composed of hydrogen, and is subsequently supplied to the power generation cell 106.
After being heated in the air preheater 103, the air is supplied to the power generation cell 106. During a stationary operation, the supply of a high temperature reformed gas and air allows the power generation cell 106 to be held in a predetermined operating temperature range between 700° C.-900° C.
The power generation cell 106 includes a plurality of single cells, and in each single cell, an electromotive force is generated through a chemical reaction. For example, a flat plate-type power generation cell includes a cell stack unit made by stacking a plurality of single cells, each of which is formed in a thin plate shape. In the cell stack unit, an electromotive force is generated through a chemical reaction in each single cell while, at a high operating temperature, a reformed gas passes through an anode side of each single cell and air passes through a cathode side of each single cell. The electromotive force is extracted from each single cell to generate electric power.
The altered, high temperature reformed gas and air exhausted from the power generation cell 106 are sent to the burner 105. In the burner 105, the reformed gas and the air are mixed to cause combustion, which heats the fuel reformer 104. An exhaust gas generated in the burner 105 is sent to the air preheater 103 to heat air by a heat exchange, and subsequently exhausted.
Specific configurations of fuel reformers are disclosed in, e.g., Patent Documents 1 and 2.
Patent Document 1 discloses a fuel reformer wherein a reforming catalyst is located in a central portion of the fuel reformer.
Specifically, a vertically oriented combustion gas passage is provided in the fuel reformer, and a reaction tube protruding downward is located in a central portion of the combustion gas passage. A combustor that generates flames is located below the reaction tube, and a protruding end portion of the reaction tube faces the combustor.
An air passage through which air passes is located around the combustion gas passage, and the reforming catalyst is provided only in the reaction tube. The reaction tube has a double tube structure. The reforming catalyst is provided only in an outer peripheral portion of the reaction tube, and not provided in the protruding end portion of the reaction tube.
Patent Document 2 discloses a fuel reformer wherein a reforming catalyst is provided in a periphery of the fuel reformer.
Specifically, a hollow cylindrical combustion chamber that accommodates a burner is installed in the center of the fuel reformer, and a cylindrical reforming catalyst layer is located around the combustion chamber.